1. Technical Field
Exemplary embodiments of the present disclosure generally relates to a reaction material and a chemical heat pump.
2. Related Art
In recent years, from the standpoint of energy conservation, heat recovery systems such as chemical heat pumps that effectively employ heat sources such as excessive exhaust heat are attracting attention.
Chemical heat pumps are systems that conduct supplying of heat and storage of heat employing exothermic and endothermic phenomenon accompanying reversible chemical reaction (hydration reaction and dehydration reaction) occurring between a reaction medium and a storage material (hereinafter referred to as reaction material). Typically, chemical heat pumps include a reactor including a heat exchanger having a reaction material reacting in a reversible manner with the reaction medium, an evaporator for evaporating a liquid reaction medium, a condenser for condensing a gaseous reaction medium, and an opening and closing mechanism that connects the reactor, evaporator, and condenser.
Specific materials as the reaction material for the chemical heat pump have been reviewed such as materials employing calcium oxide (CaO), materials employing magnesium oxide (MgO), and materials employing calcium sulfate (CaSO4). Recently, among chemical heat pumps, a chemical heat pump employing calcium oxide or magnesium oxide as the reaction material is attracting attention. For example, see JP-2010-185035-A and JP-H9-026225-A. However, in a heat pump of either JP-2010-185035-A or JP-H9-026225-A, there is a problem of decline in reaction rate of the reaction material by repeating heat storage and heat release processes.
On the other hand, when calcium sulfate is employed as the reaction material, type III anhydrous gypsum (referred to as type III calcium sulfate) is employed from the standpoint of heat storage-release properties. In heat release process, reaction heat generated by reaction of type III calcium sulfate and the reaction medium is extracted. In heat storage process, an external heat such as excessive exhaust heat is added to calcium sulfate hemihydrate (calcined gypsum) and the reaction medium is desorbed.
However, a decline of reaction rate of the reaction material is also a problem when calcium sulfate is employed as the reaction material. The decline in reaction rate when calcium sulfate is employed as the reaction material is mainly due to phase change of crystal structure of calcium sulfate. More specifically, crystal structure of type III calcium sulfate changes to a more stable crystal structure of type II anhydrous gypsum (referred to as type II calcium sulfate) by repeating heat storage and heat release processes. Thus, there is a problem of decrease in heat storage amount and heat release amount.